do ducks need a deep nest?

Hi all.
My second duck has laied alot of eggs,maybe 15 or so,but she is in a flat floored nest box and the eggs keep rolling out onto the ground.
Do ducks need a slight depression in the laying area to hold all those eggs in one place,.
I notice sometimes a few eggs are not quite underneath her also,,do they rotate the eggs for incubation or?????
Im thinking ill have to cut the bottom of the box out to accommodate her massive clutch she has.
Any help much appreciated

Last summer my pekin had 18 in her nest and everytime I went to let them out in the morning there would be three eggs out of the nest. I kept putting the eggs back in for 2 days and she kept taking them out. So I took a marker and put a tiny dot on both ends of the eggs and next day it was the same three as the day before. She kept doing it for two days until I took the eggs out. It was the same three everyday no matter where in the nest I put them. How she could tell between them I do not know. He nest was on flat ground and she build it out of straw so I really dont think your duck needs a deeper nest. You should try marking them in a not so obvious way and she if she is rolling out the same ones on purpose.